Boeing B-29 Superfortress
The B-29 was the plane that dropped THE bomb. It was plagued by engine trouble throughout its career, but no piston engine bombers were as large or as capable, and it represented the pinacle of piston-engined strategic bomber design. Finally chased from front-line combat duty by the new jet fighters, B-29's proved useful lugging around experimental aircraft.
The B-29 was the most expensive weapon of World War Two.
Cool stuff for B-29 lovers:
Check out the B-29 Superfortress T-shirt in the gift shop!